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TUBE

Filed Aug. 25; 1944 0,4900: r0 anagram}, 0F X9065 0/)2 a WITNESSES: INVENTOR ATTORNEY Patented May 17, 1949 UNITED STATES PATENT OFFICE TUBE Application August 25, 1944, Serial No. 551,124

Claims.

My invention relates to light-shielding enclosures, and, particularly, relates to such enclosures for the screen-end of cathode-ray tubes.

Cathode-ray tubes of a type widely used as indicating and measuring devices in the electrical instrument art have screens, usually in the form of a spherical segment, surfaced with phosphorescent material (i. e. with phosphors) on which incidence of a narrow cathode-ray beam inside the tube produces a luminous trace. Movement of the incidence of the cathode-ray beam over the surface of the screen traces wave forms and other contours in a manner well known to those skilled in the art. I have found in the case of certain well-known phosphors that during such motion, the beam first produces, at any point of incidence, a bright blue flash followed by an amber afterglow. The luminous intensity of the lines traced is, however, low compared to that of surfaces exposed to ordinary daylight, and it is, accordingly, necessary to shield the cathode-ray screen from incidence of stray light by means of opaque hoods or opposing walls of the like. However, in certain uses of such cathode-ray tubes, notably for navigation of airplanes, the screen of the oathode-ray tubes is surrounded by numerous dials of other instruments such as ampere meters and the like, and the use of an opaque enclosure makes it diflicult or impossible to see the latter during observation of the screen.

One object of my invention is, accordingly, to substitute for opaque-wall enclosures, such as those above mentioned, enclosing walls in the form of optical filters, transparent to light of certain wave lengths, which will not interfere with the visibility of the traces on the screen of the cathode-ray oscillograph but will still permit reading of other instruments surrounding the latter.

Another object of my invention is to provide the screen of a cathode-ray oscillograph with a filter, roughly parallel and adjacent thereto, which shall transmit light of one wave length emanating from the cathode-ray trace, for instance the above-mentioned blue flash, but which will cut off light of other wave lengths, tending to be emitted by (e. g. the amber afterglow) or reflected from the screen of the oathode-ray tube.

Other objects of my invention will become apparent upon reading the following description taken in connection with the single figure of the drawing which is a schematic representation,

showing a screen of a cathode-ray tube provided with enclosing walls and adjacent the parallel filter of the type embodying the principles of my invention.

Referring, in particular, to the drawing, a cathode-ray tube I, of which only the end adjoinin the luminous screen 2 is shown, is enclosed within a housing having walls 3 of some suitable opaque material. The screen 2 of the cathode-ray tube may be coated with phosphor (e. g. Willemite) and be surrounded by a panel 4 of some suitable opaque material having an opening through which the screen 2 projects. Alternatively the screen may be coated with a multi-layer consisting of a phosphor luminescing with one color, such as blue, mixed with or superposed on another phosphor which luminesces with another color such as orange-yellow. The colors may have different optical persistences so that, for instance, the blue may be a bright flash and the orange-yellow an afterglow. In the panel 4 may be set any desired number of indicating instruments 5, 6 for physical quantities which it may be desired to observe.

The region in front of the screen 2 may be surrounded by walls I forming a hood, comprising, in whole or in part, an optical filter which is opaque to light of the color to be observed in the trace on the screen 2 (e. g. orange-yellow), but is largely transparent to light of other colors. The light passing through the walls I will be deficient in the orange-yellow, but the colors transmitted thereby render the instruments 5, E5 plainly visible to the eye of an observer at all times. When on the other hand, the cathoderay beam traces a curve on the screen 2, the orange afterglow on the latter will be quite plainly visible because of the absence of light of those wave lengths in the incident light transmitted by the walls I and reflected by the panel d and the screen 2. The absence of these colors, when the screen is not illuminated, will render the eye of the observer more than, normally sensitive to them.

In order to supplement the desirable results produced by the enclosing walls 1, an optical filter 8 may be supported in front of the screen 2 by suitable projections 9 from the panel d. The optical screen 8 is a filter which is readily transparent to the phosphorescent color desired (e. g. orange-yellow). The filter 8 will pass the orange afterglow trace. It will, moreover, decrease the amount of stray light passing toward the screen 2 through the walls "I and reflecting from the screen 2 back into the eyes of the observer.

To give further illustrations of the application of the principles of my invention I give the following tabulation of various screen-phosphors with the filters 8 and hood 7 suitable for use with them.

fgg Visual Color Filter P-l Green 1. For general observation-green r. 2. For hooded observation-green filter and'red: hood. P-2 Blue-white l. Generalobservation blue filter. 2. Hooded use one combination blue filter and='red=hood. P-3 Yellow 1. General observation-orange or red filter. 2. Hooded-orange or red filter blue or blue-green'hood. P-5 Bluish 1. General-blue filter.

{ 2. Hooded-red hood blue filter. P-7 BlueandYellow. 1. General:

- A. For short persistence-use blue filter. 13. For long persistence-use ember or orengefilter. Screen consists of primary blue 2. Hooded: N

layer, intermediate green A. Short prs1stente-use blue coating, -fina'l yellow layer. filter, red-hood. Electron beam excites blue to B. Iaongpersistenee-use amber high'flash intensity. Blue in or orange filter,blue, or blueturn-excites yellow to longgreen hood. persistence glow.

To give specific examples of the materials of which the :filters 8 andthe walls of hood 1 maybe made, the Handbook of Chemistry and Physics, zlthedition, published by Chemical Rubber Publishin Company, Cleveland, Ohio, contains, beginning at page 2167, a tabulation of colored glasses of :American manufacture from which materials suitable for thefilter 8 :and the walls of hood 7 may. be selected. Thefollowing table identifieabycolumn headingsin-that publication, glasseswhich are respectivelysuitable 'for the fiIter'B and the walls 7.

Phosphor Filter Walls BL Green 19.. (JG-244 BLBlue'O.-. OG-244 OG-2 BL Green 19-. BL Blue 0.... -CG-244 BL Blue 0...; 6-244 To observe-short persistence trace.

OG-2 BL Bluc 19". To observe long persist once trace.

While I have describedthefilter '8jas a supple- 'menttothe' enclosing walls I, it'willbe recognized that under some circumstances it-may be desirable for economic or other reasons to omit the hood I and employ only the filter-8, or toomit the filter 8 and employonlyhood 7.

While 'I have described a particular embodiment of the principles of my invention to comply with particularstatutes, it will be recognized '4 that these principles are applicable in other ways which will be apparent to those skilled in the art.

I claim as my invention:

1. In combination with a cathode-ray tube, having a fluorescent screen on which a cathoderay beam produces a trace of predetermined color, an optical path over which an observer can view said screen, -'enclosingwalls :about said path consisting at 'least in partpf a material, having substantially higher opacity to said color than it has to other colors.

2. In combination with a cathode-ray tube, having a screen coated with willemite, an optical .-pathover=whichanobserver can view said screen,

enclosingwallseibout said path, consisting at least "inpa'rt'ofan area of material which is opaque to an optical path over whichia'n observer can-view said'screen andconsisti-ng :atvleast in part "ofa material which is moretran'spairent to medili'ght "than to light in other :portions of the spectrum.

- 4.-An enclosingmchamber for :the screen of-a cathode-ray tube coated with willemita'comprising enclosingwalls surrounding an optical path over which'an observer can'view-said screen and consisting at least in part'of an area of material more highly transparent rto light in other portions 'of the spectrumthan to light or the blueegreen portion.

5. An enclosure for a -cathode-ray 'tube'which has a fluorescent screen emitting light=of1s one color when bombarded with electrons;-.said enclosure having all portions surrounding :an optical path over which an observer can 'viewisaid screen'which is lesstransparent to said one color than to other colors.

FREDERICK G.-SUFFIELD.

REFERENCES CITED The following references are of record -in t-he *file of this patent:

UNITED STATES PATENTS Number Name Date 1,691,324 A Zworykin Nov. 13, 1928 2.015570 Sabbah-et a1 -Sept. 24 ;1'935 2,026,725 Baker .'.--Jan.. 5 1 936 2,051,632 'Batchelor -Aug. "18, @1936 2,312,206 -Calb'ick Feb.23, l 943 2,402,762 Leverenz June -25, 1946 FOREIGN PATENTS Number Country 'Da'te 395,578 GreatiBritain July "20; 1933 426,789 Great Britain Apr; 5;1985 426,797 Great Britain Apr. 10'," 1935 ;978 Great Britain. Dec.'20,---I935 

